[gegl] buffer: more improvements to sampler box filtering

[N/A <ell src gnome org>]

commit 2529e036f1b49300ec86392291fdd899e2d52178
Author: Ell <ell_se yahoo com>
Date:   Sat Mar 3 04:29:17 2018 -0500

    buffer: more improvements to sampler box filtering
    
    In _gegl_sampler_box_get(), clamp coordinates to avoid integer
    overflow, and avoid division by 0 when no samples are taken, which
    can happen when the bounds of the sampled area are clamped.  In
    particular, this can happen in perspective transforms where one of
    the transformed vertices is close to the horizon.

 gegl/buffer/gegl-sampler.h |   29 +++++++++++++++++++----------
 1 files changed, 19 insertions(+), 10 deletions(-)
---
diff --git a/gegl/buffer/gegl-sampler.h b/gegl/buffer/gegl-sampler.h
index 1b23f03..e482a7f 100644
--- a/gegl/buffer/gegl-sampler.h
+++ b/gegl/buffer/gegl-sampler.h
@@ -239,14 +239,18 @@ _gegl_sampler_box_get (GeglSampler*    restrict  self,
                               MAX (0.0, scale->coeff[1][0] + scale->coeff[1][1]));
       const gdouble w = x2 - x1;
       const gdouble h = y2 - y1;
-      const gint ix = floor (absolute_x - w / 2.0);
-      const gint iy = floor (absolute_y - h / 2.0);
-      const gint xx = ceil  (absolute_x + w / 2.0);
-      const gint yy = ceil  (absolute_y + h / 2.0);
+      const gdouble ixf = floor (absolute_x - w / 2.0);
+      const gdouble iyf = floor (absolute_y - h / 2.0);
+      const gdouble xxf = ceil  (absolute_x + w / 2.0);
+      const gdouble yyf = ceil  (absolute_y + h / 2.0);
+      const gint ix = CLAMP (ixf, -(G_MAXINT / 2), +(G_MAXINT / 2));
+      const gint iy = CLAMP (iyf, -(G_MAXINT / 2), +(G_MAXINT / 2));
+      const gint xx = CLAMP (xxf, -(G_MAXINT / 2), +(G_MAXINT / 2));
+      const gint yy = CLAMP (yyf, -(G_MAXINT / 2), +(G_MAXINT / 2));
       int u, v;
       int count = 0;
-      int hskip = w / n_samples;
-      int vskip = h / n_samples;
+      int hskip = (xx - ix) / n_samples;
+      int vskip = (yy - iy) / n_samples;
 
       if (hskip <= 0)
         hskip = 1;
@@ -268,10 +272,15 @@ _gegl_sampler_box_get (GeglSampler*    restrict  self,
               count ++;
             }
         }
-      result[0] /= count;
-      result[1] /= count;
-      result[2] /= count;
-      result[3] /= count;
+
+      if (count)
+        {
+          result[0] /= count;
+          result[1] /= count;
+          result[2] /= count;
+          result[3] /= count;
+        }
+
       babl_process (self->fish, result, output, 1);
 
       return TRUE;